Currently, there are many kinds of computer mouse available on the market, which are the most popular human-machine interface used by computers as cursor-control device. There are three basic types of mice, which are mechanical mouse, LED optical mouse and laser mouse with respect to the different means of detection. A typical mechanical mouse comprises a chassis containing a ball, with a part of the ball protruding through the underside of the chassis. When an user moves the mouse about on a flat surface, the ball rotates which is detected by the sensors arranged in the chassis. Unfortunately the moving parts of such a mouse can become dirty, causing the sensors to incorrectly measure ball rotation. A typical LED optical mouse has a small, red light-emitting diode (LED) that bounces light off that surface with sufficient roughness onto a complimentary metal-oxide semiconductor (CMOS) sensor. The CMOS sensor sends each image to a digital signal processor (DSP) for analysis, that the DSP is able to detect patterns of shadows generated by the roughness of the surface in the images and see how those patterns have moved since the previous image. Based on the change in patterns over a sequence of images, the DSP determines how far the mouse has moved and sends the corresponding coordinates to the computer. However, if the working surface of the LED optical mouse is a smooth surface made of marble, tile, or metal, etc., such mouse might not be able to operate without a hitch. A laser mouse is an advanced optical mouse, which is capable of emitting a coherent light so as to detect more surface pattern variation than the standard LED based optical mice. Nevertheless, such laser mice are not able to operate fluently while working on a transparent surface made of glass, acrylic, and so on.
Since most conventional computer mice are disadvantageous as stated above, it is popular to have an inertial sensing module embedded inside a pointing device for using the inertial sensing module to detect and measure movements of the pointing device operating while sitting on a flat surface or being held in a free space. However, as an integration operation is performed by the inertial sensing module when it is being used for detecting and measuring displacement of the pointing device operating while sitting on a surface so as to control the movements of a cursor displayed on a displaying device, certain noises corresponding to the displacement will be amplified by the integration operation that causes difficulties to control and move the cursor accurately on the displaying device. There are already several researches developed or solving the noise problem. One of which is an inertial pointing device disclosed in TW Pat. No. 0519263. The foregoing inertial pointing device uses accelerometers to determine the accelerations of the inertial pointing device, and then uses an adjustable digital low-pass filter to process the signals of detected accelerations so that noises corresponding to the acceleration signals can be eliminated and the control of the cursor is improved. However, since the digital filtering performed by the low-pass filter requires a high sampling frequency, an user holding the inertial pointing device will suffer a sluggish feeling that is not felt by using an analog filtering. In addition, for storing the enormous amount of coefficients and numerical values required and generated by the digital low-pass filter, a massive memory is required so that the cost and load of the inertial pointing device are increased.
Therefore, what is needed and would be useful is a signal processing method and apparatus that can free a pointing device using the same from the aforesaid problems.